The level of comfort in an inside space is related to both temperature and humidity. While temperature control has long been a primary focus of many HVAC systems, humidity control is becoming ever more important. When an air conditioner is operating at steady state, air flowing past the air conditioner coils generally results in condensation on the coils, thus removing water from the air and reducing the humidity of the inside space.
However, when many air conditioners are first activated, and for a time period thereafter, the temperature of the air conditioner coils is above the dew point temperature of the air. That is, the air conditioner coils have not yet had time to cool to a temperature that is below the dew point temperature of the air in the inside space. Accordingly, when the air conditioner is first activated, and for a time period thereafter, little or no latent cooling (i.e. moisture removal) occurs. Rather, the air conditioner must remain “on” for a period of time before the temperature of the air conditioner coils can drop below the dew point temperature of the air, and begin removing water from the air.
This is particularly problematic when the cooling capacity of the air conditioner is large relative to the cooling demands of the inside space. In some cases, the air conditioner is simply oversized for the size of the inside space, and in other cases, the environmental conditions only present a limited heat load to the air conditioner. In either case, the air conditioner typically may satisfy a call for cooling in a relatively short time period, which may result in relatively short duty cycles. To prevent very short duty cycles, which could damage the air conditioner, many manufacturers specify a minimum “on” time for their air conditioning units. However, because the minimum “on” time is specified for a different purpose (e.g. to prevent damage), the minimum “on” time requirement is typically too short (e.g. 3 minutes or less) to allow for any significant water removal during this period. For these and other reasons, it has been found that existing control algorithms that attempt to moderate or reduce humidity using an air conditioner, particularly when the air conditioner is under low or moderate load conditions, are not very effective.